A mapping of subclasses of Exception
to wire-protocol tags for errors represented as strs.
Responders which raise keys from this dictionary will have the error
translated to the corresponding tag on the wire. Invokers which receive
Deferreds from invoking this command with AMP.callRemote will
potentially receive Failures with keys from this mapping as their value.
This mapping is inherited; if you declare a command which handles
FooError as 'FOO_ERROR', then subclass it and specify
BarError as 'BAR_ERROR', responders to the subclass may raise
either FooError or BarError, and invokers must be
able to deal with either of those exceptions.

a boolean; defaults to True. Set it to False on your subclass if you want
callRemote to return None. Note: this is a hint only to the client side of
the protocol. The return-type of a command responder method must always be
a dictionary adhering to the contract specified by response,
because clients are always free to request a response if they want one.